Drivers, especially those who own 'gas guzzlers', are coming under increasing pressure to switch to low-carbon-emitting cars. Although the Chancellor postponed a 2p increase in fuel duty until October, every other vehicle-related measure announced in last week's Budget was aimed at reducing fuel consumption.

Alistair Darling not only raised the prospect of road pricing again, promising funding for further pilot schemes, but also increased road tax on the most polluting vehicles. While the most environmentally friendly vehicles will incur no tax at all, from 2010 the buyers of brand-new high-emitting 4x4s, sports cars and saloons will have to pay vehicle excise duty of £950 in the first year (the so-called 'showroom tax'). Thereafter, road tax for such cars will cost £455 a year, compared with £300 now.

Currently there are six road tax bands for cars registered in the last seven years, based on their emissions: electric cars such as the G-Wiz are free, while many vehicles in band G pay the £300 rate (£400 in the 2008/09 tax year). From April 2009, the Budget extends this regime further with new bands H to M, which face further increases.

Louise Marix Evans runs her own consultancy business on sustainable development, and therefore welcomes moves to encourage drivers to use more economical cars. She and her husband Chris Sylge run a W-reg Vauxhall Astra estate and an old Corsa, but have already thought about switching to a more carbon-efficient car and signing up to a car club scheme.

'When I looked at our household budget, our cars were stonkingly expensive,' Louise says. She and Chris are waiting for cars with with the lowest carbon emissions to come through to the second-hand car market at an affordable price. The Citroen C3 (band B, £35 road tax this year) is their preferred choice, if they can find one.

Louise welcomes higher duties for gas-guzzlers but is sceptical that this will necessarily change habits. 'They are being driven as status symbols,' she says. 'The extra duty may just make people think the drivers are even richer.'

Louise also welcomes talk of wider measures against climate change, but isn't convinced that the government means action. The couple live in an old house in a small Pennine village in Yorkshire with their two daughters, Cherry, aged 5, and Olivia, aged 3, and are considering having a new solar panel installed. But as Louise points out, she will still have to pay 5 per cent VAT on it.

There was, however, one part of the Budget speech that spoke directly to her. Darling warned that the government would introduce legislation to deal with the vast numbers of plastic carrier bags given out by supermarkets if retailers do not voluntarily introduce charges to deter shoppers from using them. Louise campaigned successfully last year for her town to become plastic-bag free, and she's delighted that this is now a national issue. 'This has been a grass-roots campaign, and the government is saying "we'll back you up",' she says.